Let, digital cameras be "x" video cameras be "y" Now, According to the question, 5x + 3y = $3,213..................................................equation (1) y = 4x..................................................................equation (2)
Taking equation (1) 5x + 3y = $3,213 Substituting the value of "y" from equation (2), we get, 5x + 3(4x) = $3,213 5x + 12x = $3,213 17x = $3,213 x = $3,213 / 17 x = $189
Taking equation (2) y = 4x Substituting the value of "x", we get, y = 4 ($189) y = $756
Now, John buys a digital and a video camera. So, it costs him ($189 + $756) = $945